Diamond grains are typically used for the production of diamond tools such as grinding wheels, dressing or truing tools for grinding wheels, and saw blades.
To function effectively and efficiently in certain tool applications, particularly applications requiring diamond saw blades, diamond grit having the highest strength (including high temperature strength), toughness, and abrasion resistance is often desirable. Techniques for bonding diamond to saw blades include the utilization of nickel, cobalt, iron, and other metals and/or alloys for sintering at elevated temperatures from 600 to approximately 1300 degrees Centigrade. At these temperatures, the strength of the diamond may deteriorate. In a vacuum, mild surface graphitization of diamond begins at temperatures above about 1000 degrees Centigrade. In air, diamond will begin to oxidize at about 600 degrees Centigrade. At temperatures above 900 degrees Centigrade, catalyst residues can lead to the regraphitization of diamond or partial disintegration of the crystal due to the relatively large thermal expansion of these metal residues.
U.S. Pat. No. 5,035,771 to Borse describes a process where diamonds in a iron, cobalt, or nickel powder are exposed to a hydrogen atmosphere at a temperature above 700 degrees Centigrade to etch pores in the surface of the diamond to give a roughened surface for enhancing the bonding of the diamond to a saw or grinding wheel. As set forth in column 4, lines 50 to 52, temperatures above 900 degrees Centigrade are disadvantageous because the internal strength of the diamonds is reduced. U.S. Pat. No. 4,174,380 to Strong et al relates to annealing diamond at a temperature ranging from 1500 to 2200 degrees Centigrade under a pressure which prevents graphitization. This process was designed not to improve diamond strength, but rather to aggregate atomically dispersed nitrogen to change the diamond color properties.
A number of researchers have attempted to improve grit diamond strength by heat treating (see Field, 1992, for overview),. Dyer and Conradi (1972) report reducing the toughness index (TI) and thermal toughness index (TTI) test strengths of synthetic diamond after heating to 1400 K. Muhkin et al (1974) and Simkin (1982) also reported strength loss in heating synthetic diamond. Uvarov et al (1974) reported a strength increase for natural diamond as measured by uniaxial compression test upon heating at temperatures between 1300 and 1,880 degrees Kelvin.
The focus of the prior art is that high temperature treatment of diamonds in various gaseous atmospheres must be performed under very carefully controlled conditions to avoid degradation of diamond. Hence, any process for treating diamond grit of the type use for diamond tools which results in increased strength as measured by toughness and strength test represents an advance in the art.